1. Field of the Invention
The present invention relates to a golf ball and more particularly to an improvement in a dimple pattern of the golf ball.
2. Description of the Related Art
A golf ball has approximately 200 to 550 dimples on a surface thereof. The role of the dimples resides in one aspect that such dimples disturb an air stream around the golf ball during the flight of the golf ball to accelerate the transition of a turbulent flow at a boundary layer, thereby causing a turbulent flow separation (which will be hereinafter referred to as a xe2x80x9cdimple effectxe2x80x9d). The acceleration of the transition of the turbulent flow causes a separating point of air from the golf ball to be shifted backward so that a drag coefficient (Cd) is reduced, resulting in an increase in the flight distance of the golf ball. Moreover, the acceleration of the transition of the turbulent flow increases a differentia between upper and lower separating points of the golf ball which is caused by a back spin. Consequently, a lift acting on the golf ball is increased.
There have been proposed various golf balls having improved dimple patterns in order to enhance a flight performance. For example, Japanese Patent Publication No. Sho 58-50744 (1983/50744) (U.S. Pat. No. 4,936,587 and U.S. Pat. No. 5,080,367) has disclosed a golf ball in which dimples are densely provided such that a pitch between the dimples is 1.62 mm or less if possible. Moreover, Japanese Unexamined Patent Publication No. Sho 62-192181 (1987/192181) (U.S. Pat. No. 4,813,677) has disclosed a golf ball in which dimples are densely provided so as not to form a new dimple having an area which is equal to or larger than a mean area in a land portion other than the dimples. Furthermore, Japanese Unexamined Patent Publication No. Hei 4-347177 (1992/347177) (U.S. Pat. No. 5,292,132) has disclosed a golf ball in which dimples are provided very densely such that the number of land portions in which a rectangle having a predetermined dimension can be drawn is 40 or less.
All the golf balls disclosed in the publications have dimples provided densely, in other words, the surface area occupation ratio of the dimples is increased. The person skilled in the art has recognized that the surface area occupation ratio is one of important elements to influence a dimple effect.
However, the surface area occupation ratio is not the only index to guess the dimple effect. In order to further enhance the flight performance, an improvement in a dimple pattern is to be investigated together with the surface area occupation ratio in other respects.
The present inventors have taken note of a total length of dimple contours (hereinafter referred to as a xe2x80x9ctotal contour lengthxe2x80x9d) in addition to the surface area occupation ratio as an important element to influence the dimple effect. The present inventors have found that a smaller total contour length tends to be more excellent in a flight performance if the surface area occupation ratio is equal in an existing golf ball. By setting the relationship between the surface area occupation ratio and the total contour length to a range which cannot be obtained by the existing golf ball, the flight performance could be enhanced.
The present invention provides a golf ball having a large number of dimples on a surface thereof, wherein X and Y satisfy a relationship of an equation (I):
Xxe2x89xa63882xc2x7Y+1495xe2x80x83xe2x80x83(I),
X representing a total of dimple contour lengths x and Y representing a surface area occupation ratio of the dimples.
The golf ball having the total contour length X and the surface area occupation ratio Y to satisfy the equation (I) comprises a dimple pattern having the small total contour length X for the surface area occupation ratio Y. The reason why the flight performance of the golf ball is excellent is not clear in detail. It is guessed that the dimple pattern contributes to a reduction in a drag coefficient (Cd), particularly, a reduction in the drag coefficient (Cd) in a high-speed region immediately after hitting.
It is preferable that the surface area occupation ratio Y should be 0.70 to 0.90. Consequently, the flight performance of the golf ball can further be enhanced.
It is preferable that the number of dimples having the contour length x of 10.5 mm or more should be 91% of the total number of the dimples or more. Consequently, the flight performance of the golf ball can be enhanced still more.